1. Field of the Invention
The present invention relates to a technique for recording an image on a photosensitive material by irradiation with light.
2. Description of the Background Art
Developed has been a spatial light modulator of diffraction grating type which is capable of changing the depth of grating by alternately forming fixed ribbons and moving ribbons on a substrate with a semiconductor device manufacturing technique and deflecting the moving ribbons relatively to the fixed ribbons (that is to say, moving the reflective surfaces of the moving ribbons). It is proposed that such a spatial light modulator is used in various fields such as CTP (Computer to Plate) as a high-speed switching element of light over a wide range of wavelength, since the intensities of regular reflection light and diffracted light are changed by changing the depth of grooves on the spatial light modulator as above.
For example, in an image recording apparatus disclosed in Japanese Patent Publication No. 3530157 (Document 1), a spatial light modulator of diffraction grating type is irradiated with light, and then reflected light beams (zeroth order light beams) from portions in a state where the fixed ribbons and the moving ribbons are positioned at the same height from a base surface on the spatial light modulator are guided to a photosensitive material and non-zeroth order diffracted light beams (mainly first order diffracted light beams) from portions in a state where the moving ribbons are deflected are blocked, to achieve an image recording on the photosensitive material.
U.S. Pat. No. 4,879,605 (Document 2) and “Image quality enhancements for raster scan lithography” (Document 3) (Michael L. Rieger et al., SPIE vol. 922, Optical/Laser Microlithography, pp. 55-64, 1988) disclose a method where respective irradiation regions are set with their centers lying at positions on a photosensitive material and partially overlapping with adjacent irradiation regions, and writing is performed by irradiation with light onto each irradiation region. In the method, an amount of light applied onto each of specified irradiation regions is varied to make a variable unit of edge position of photosensed area on the photosensitive material (hereat, the photosensed area is an area where a part of photosensitive material is changed in nature) smaller than the center-to-center distance between two adjacent irradiation regions (that is to say, addressable resolution (positional resolution) goes up).
In a spatial light modulator for a general image recording apparatus, out of a plurality of ribbon pairs each of which is a combination of one fixed ribbon and one moving ribbon, continuous six ribbon pairs are determined as a unit of modulation control (see Document 1, for example) and United States Patent Application Publication Ser. No. 2004/0036950 discloses a spatial light modulator of diffraction grating type for independently controlling each of the plurality of ribbon pairs (where one ribbon pair is determined as a unit of modulation control). In a general display with the spatial light modulator of diffraction grating type, continuous three ribbon pairs out of the plurality of ribbon pairs are a unit of modulation control.
In the method of Document 2 and 3, normally, the rate of change of accumulated light amount of irradiation light decreases in the vicinity of edge position of the photosensed area on the photosensed material (i.e., the boundary blurs) and the edge position of actual photosensed area (or line width) on the photosensitive material greatly changes, even if the light amount for photosensing of the photosensitive material slightly varies depending on various conditions for image recording such as environment conditions. This problem particularly arises in a photosensitive material with small gamma value.